1. Field of the Invention
The invention relates to a spring and shock absorber unit for air-suspended vehicle axles having a U-type bellows air spring which is supported on one side relative to the vehicle frame and on the other side relative to the vehicle axle or a longitudinal control arm guiding the vehicle axle. The U-type bellows is fastened on the longitudinal control arm side in a pressure-tight manner to a supporting element, and a vibration absorber arranged on the longitudinal axis of the air spring protrudes through the supporting element. The piston cylinder of the vibration absorber is connected to the longitudinal control arm via a joint and the piston rod is supported relative to the vehicle frame.
2. Description of the Related Art
A spring and shock absorber unit having these features is disclosed in DE 199 59 839 A1. It first of all comprises a U-type bellows air spring which is fastened to the vehicle frame in a manner known per se via a trunk piston, along which the U-type bellows can roll, on a chassis part guiding the vehicle axle, and via an upper closing cover. The particular feature of the spring and shock absorber unit according to DE 199 59 839 A1 is that a vibration absorber is structurally integrated in the air spring, which is of largely conventional construction. In this case, the piston cylinder of the vibration absorber is, for the most part, situated centrally within the trunk piston of the air spring, whereas the piston rod protrudes through the air space of the air spring and is supported with its end relative to the vehicle frame. If the vibration absorber were connected fixedly on one side to the chassis parts and on the other side to the vehicle frame, bending and therefore tilting of the vibration absorber would occur during the compression action. In order to avoid this, the piston rod of the vibration absorber is articulated relative to the vehicle frame and the piston cylinder is articulated relative to those vehicle parts to which it is fastened. For this purpose, the piston cylinder is arranged in a manner such that it can be moved at an angle in the trunk piston by means of a pivot bearing. However, the articulation ability of the piston cylinder realized in this manner must not result in air escaping from the air spring via the joint, which is exposed on its one side to the full air pressure of the air spring. For this reason, the joint has at least one additional sealing ring which seals the air volume in the spring space.
Since the sealing ring has to join in with the pivoting movements of the vibration absorber in the driving mode, it is subject to a high degree of wear, which forces frequent replacement of the sealing ring, which is difficult to gain access to.
The invention is based on the object of providing a spring and shock absorber unit which is improved with regard to the sealing between the vibration absorber and air spring.
This object is achieved by arranging the supporting element for the lower end of the U-type bellows rigidly with respect to the piston cylinder of the vibration absorber.
In the case of the spring and shock absorber unit according to the invention, not only does the vibration absorber pivot with respect to the longitudinal control arm, but so too does part of the air spring, specifically that supporting element to which the U-type bellows of the air spring is fastened in a pressure-tight manner on the longitudinal control arm side. There is a rigid connection between the vibration absorber, on the one hand, and the supporting element of the air spring, on the other hand, these two parts therefore together following each compression and rebound movement of the vehicle. Owing to the rigid arrangement of the supporting element of the air spring with respect to the piston cylinder of the vibration absorber, the sealing of these two parts with respect to each other only has to meet undemanding requirements. Although sealing is necessary in order to prevent the compressed air from escaping from the air spring, the sealing between two parts which cannot be moved relative to each other is not mechanically stressed and is therefore not critical.
With a preferred refinement of the spring and shock absorber unit, it is proposed that the supporting element has at least one flange which surrounds the vibration absorber and to which the lower end of the U-type bellows is fastened in a pressure-tight manner, and that a preferably cylindrical circumferential surface for the U-type bellows to roll along during the compression and rebound action extends from the flange toward the longitudinal control arm. In this refinement, the flexible U-type bellows can roll in a controlled manner along the preferably cup-shaped trunk piston. In order to obtain a structurally simple design of the trunk piston, the flange and circumferential surface are parts of a cup which is open downward toward the longitudinal control arm.
The joint, via which the vibration absorber is mounted pivotably on the longitudinal control arm, is preferably surrounded by the circumferential surface which has an axial height extending from the flange. The joint is preferably situated at approximately half the axial height of the circumferential surface.
With a further refinement, it is proposed that that part of the joint which is on the air spring side is situated on a rigid sleeve surrounding the piston cylinder, and that both the piston cylinder and the supporting element are fastened to the sleeve. This permits a construction with just a few individual parts, since the sleeve takes on a dual function. Both the vibration absorber and the supporting element of the air spring are fastened to it.
In order to keep any bending moments on the vibration absorber as low as possible, with a further refinement of the invention, the axis of rotation of the joint intersects the longitudinal axis of the vibration absorber at a right angle. The joint may also be, for example, a spherical ball socket as is disclosed in FIG. 6 of DE 199 59 839 A1.
With a further refinement, that part of the joint which is on the longitudinal control arm side is situated on a fork which is part of the longitudinal control arm, and the piston cylinder is arranged pivotably between the two halves of the fork. The fork, first of all, permits a particularly weight-saving manner of construction, this being of importance, since the longitudinal control arm and hence also the fork are included in the unsuspended masses of the chassis. In addition, the fork permits the head wind to pass in an unobstructed manner to the vibration absorber arranged between the two fork halves and thereby permits it to cool the piston cylinder of said vibration absorber.
The fork is preferably composed of an essentially horizontal fork section, which forms an extension of the longitudinal control arm, and of a fork end which is arranged at right angles to said fork section and on which that part of the joint which is on the longitudinal control arm side is situated.
The piston cylinder is preferably provided in the region of its end facing the piston rod with a collar which fixes the piston cylinder relative to compressive and tensile forces in the air spring.
During operation, vibration absorbers tend to generate a considerable amount of heat. In order to better conduct this heat away, it is proposed, with a further refinement, that the piston cylinder is extended at its end facing away from the piston rod to such an extent that the extended section of the piston cylinder protrudes from the air spring.
On account of the considerable spring deflections, it is advantageous if the piston rod is a two-stage telescopic piston rod.
In order to obtain a small overall height of the entire spring and shock absorber unit, the upper end of the U-type bellows is fastened in a pressure-tight manner to a cover which, for its part, can be fastened to the vehicle frame. The cover is provided with a central part which projects in a cup-like manner in the direction of the air spring and on the base of which the end of the piston rod is supported in a pressure-tight manner.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.